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Hydrogel backbone Scientists in Australia have developed a stronger hydrogel material which could eventually be used for spinal cord replacements and as a synthetic human cartilage.

The research led by Associate Professor Marc in het Panhuis from the University of Wollongong, also has applications in soft robotics, used for research and rescue operations in tight places.

The study, reported in the Royal Society of Chemistry's journal Soft Matter, combined two existing polymers, gellan gum and polyacrylamide, to produce the new material called an ionic-covalent entanglement gel.

The tough new hydrogel can recover from large strains and absorb impacts without permanent damage.

Hydrogels are soft and wet materials comprising up to 95 per cent water with the molecules encased in a polymer cage.

According to in het Panhuis hydrogels are playing an increasingly important role in human tissue engineering.

"However they easily lose their strength, restricting their use to items which don't place them under mechanical stress."

Broken bonds

While their mechanical properties can be increased by combining two polymer materials into the one gel, they can only be deformed once because the covalent bonds holding the molecules together break during deformation.

In het Panhuis and colleagues tackled the problem by developing a hydrogel that included molecules held together by ionic bonds.

"These let you repeatedly deform the hydrogel material because the ions are pushed apart during deformation, but gradually recover and come back together again," he says.

Covalent bonds occur where atoms share electrons while ionic bonds happen when electrons are removed from one atom and attached to another, resulting in positive and negative ions that attract each other.

Challenges ahead

In het Panhuis says testing shows durability and toxicity isn't an issue, but the team still needs to tweak the material to make it tough enough for use as a cartilage replacement, and to ensure it holds together in the human body.

They also need to develop a way of making it electrically conductive for spinal cord replacement and soft robotics.

"We need to find a way of getting the electrical component to work in the watery hydrogel environment," says in het Panhuis.

"Other teams at the University of Wollongong are working on this and we're making great strides."

Competition

Three days after the publication of in het Panhuis and colleagues research, another team released details of similar hydrogel research the journal Nature.

"They used a polyacrylamide made differently and combined it with a polymer alginate, giving it different properties to ours," says in het Panhuis.

"The Nature report demonstrates a really tough hydrogel, but it recovers best at 80°C which isn't practical for use in a human body."